Activation of phosphatidylinositol 3-kinase by cellular prion protein and its role in cell survival Neville Vassallo a,b, * ,1 , Jochen Herms b,1 , Christina Behrens c , Bjarne Krebs b , Keiichi Saeki d , Takashi Onodera d , Otto Windl e , Hans A. Kretzschmar b a Department of Physiology and Biochemistry, University of Malta, Msida MSD 06, Malta b Zentrum fu ¨ r Neuropathologie und Prion Forschung, Ludwig Maximilians Universita ¨ t, Feodor-Lynen-Str. 23, 81377 Munich, Germany c Institut fu ¨ r Neuropathologie, Georg-August Universita ¨t, Go ¨ ttingen, 37075 Gottingen, Germany d Department of Molecular Immunology, School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku 113-8657, Japan e TSE Molecular Biology, Veterinary Laboratories Agency, Weybridge Woodham Lane, Surrey KT15 3NB, UK Received 15 April 2005 Available online 27 April 2005 Abstract The cellular prion protein (PrP C ) is thought to be involved in protection against cell death, however the exact cellular mechanisms involved are still controversial. Herein we present data that strongly indicate a functional link between PrP C expression and phos- phatidylinositol 3-kinase (PI 3-kinase) activation, a protein kinase that plays a pivotal role in cell survival. Both mouse neuroblas- toma N2a cells and immortalized murine hippocampal neuronal cell lines expressing wild-type PrP C had significantly higher PI 3-kinase activity levels than their respective controls. Moreover, PI 3-kinase activity was found to be elevated in brain lysates from wild-type mice, as compared to prion protein-knockout mice. Recruitment of PI 3-kinase by PrP C was shown to contribute to cel- lular survival toward oxidative stress by using 3-morpholinosydnonimine (SIN-1) and serum deprivation. Moreover, both PI 3-ki- nase activation and cytoprotection by PrP C appeared to rely on copper binding to the N-terminal octapeptide of PrP C . Thus, we propose a model in which the interaction of copper(II) with the N-terminal domain of PrP C enables transduction of a signal to PI 3-kinase; the latter, in turn, mediates downstream regulation of cell survival. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Prion protein; Phosphatidylinositol 3-kinase; Copper; Cellular survival; Oxidative stress The cellular prion protein (PrP C ) is a glycosylphos- phatidylinositol (GPI)-anchored membrane protein that is highly conserved in mammalian species [1]. The mol- ecule is expressed most abundantly in the brain, but has also been detected in other non-neuronal tissues as diverse as lymphoid cells, lung, heart, kidney, gastroin- testinal tract, muscle, and mammary glands [2,3]. Although PrP C is likely to have a basic biological func- tion in cells, its precise physiological role is still un- known. Over the past years, evidence has been accumulating consistent with an involvement of PrP C in signal transduction pathways [4]. This is not surpris- ing as PrP C is targeted to cholesterol-rich microdomains of the plasma membrane, regions that are abundant in receptors and signaling molecules [5] Another well-stud- ied aspect of PrP C is its ability to selectively bind copper(II) ions via an octarepeat domain in the N-termi- nal region [6,7]. Several studies have indicated that deletion of this domain (consisting of four sequential copies of the sequence PH GGGWGQ) interferes with PrP C function [8–10]. In addition, the capacity of PrP C to interact with superoxide ions and hydrogen peroxide has been found to be copper-dependent [11]. Hence, copper(II) binding also confers redox properties to the 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.04.099 * Corresponding author. E-mail address: neville.vassallo@um.edu.mt (N. Vassallo). 1 These authors contributed equally to this work. www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 332 (2005) 75–82 BBRC